Radiofrequency probes for tissue treatment and methods of use

ABSTRACT

A device and method for radiofrequency treatment of tissue is disclosed. The device includes an introducer, a plurality of RF electrodes positionable in a nondeployed state within the introducer, and an electrode advancement element. In the nondeployed state, the RF electrodes are contained within the introducer, and separated from the subject&#39;s tissue by a plug which substantially occludes the distal end of the introducer. In the method for RF tissue treatment, the introducer is introduced into the tissue of a subject. The RF electrodes are then positioned in the deployed state when the electrode advancement element advances the RF electrodes through the distal end of the introducer, thereby displacing the plug. The electrode advancement element may be a spring-loaded element, and may be actuated by a triggering device on the introducer. The introducer and the RF electrodes may be scored to enhance their visibility in medical imaging studies such as ultrasound, thereby helping to ensure optimal placement of the introducer and the RF electrodes.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Stage of International Application No.PCT/US01/20632, filed Jun. 28, 2001, which was published in Englishunder PCT Article 21(2), which in turn claims the benefit of U.S.Provisional Application No. 60/217,033, filed Jul. 10, 2000. Bothapplications are incorporated herein in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to radiofrequency probes fortissue ablation, and more particularly to improved probes and methodsfor using such probes in reducing tissue volume.

BACKGROUND OF THE INVENTION

Application of radiofrequency (RF) energy has emerged as an importantapproach to eliminating or reducing the size of undesirable tissue in asubject. When properly directed and localized, RF energy causescontrolled hyperthermia that damages or destroys the undesirable tissuewithout injuring surrounding tissue. For example, RF energy has beenused to treat tumors such as metastatic cancer lesions in the liver, toimprove obstructive breathing disorders by increasing airway size, andto eliminate undesirable electrical conduction pathways in the heart.See Hyman, Dis. Colon Rectum 43: 279 (2000); Powell et al., Chest 113:1163-1174; Man et al., Journal of the American College of Cardiology 35:451-457 (2000); U.S. Pat. Nos. 5,728,094; and 5,849,028, all of whichare herein incorporated by reference in their entirety.

RF energy may be used during minimally invasive procedures. For example,RF electrodes may be placed percutaneously (through the skin) to treat ametastatic cancer lesion in the liver. Such a procedure usually requiresonly local anesthesia with or without conscious sedation. The targetlesion may be localized and appropriate RF electrode placement confirmedby standard medical imaging techniques such as ultrasound. Applicationof measured amounts of RF energy partially or completely destroys thetumor. Using such minimally invasive procedures, it is often possible totreat a subject and discharge him in the same day. In contrast, an open(full surgical) procedure usually requires general anesthesia and manydays to weeks of inpatient recovery.

Recently, RF devices have been developed that may be deployed as an RFelectrode array. For example, U.S. Pat. No. 6,071,280, hereinincorporated by reference, discloses an array of deployable RFelectrodes contained within a delivery catheter. The tip of the deliverycatheter is inserted in the tissue, for example percutaneously, andproperly positioned near the ablation target. The RF electrodes aremanually advanced out of the delivery catheter into the target tissue.On deployment, the RF electrodes fan out into an array that defines thevolume of tissue to be ablated by RF energy. Similarly, U.S. Pat. No.5,827,276, herein incorporated by reference, discloses an RF electrodewire array contained within a delivery catheter. Upon catheterinsertion, the RF electrode wires are manually advanced out of thecatheter and properly positioned within the target tissue.

SUMMARY OF THE DISCLOSURE

Although these prior uses of RF have undeniable utility, severalproblems remain. First, there is a significant risk of tissue orvascular injury during placement of the RF electrodes. Usually, this isattributable to a “coring” effect from the open distal end of thedelivery catheter (through which the RF electrodes are advanced into thetissue). Such injury may lead to an emergency surgical procedure, oreven death of the subject. Second, after RF electrode deployment it isoften difficult to precisely determine the location of the probe tips.This may lead to incorrect placement, with inadequate treatment of thetarget and/or damage to surrounding normal tissue. Third, presentlyavailable devices require the operator to manually advance the probetips from the delivery catheter into the tissue. Thus, the operator isrequired to use both hands to operate the RF tissue ablation device. Inaddition, in unusually hard or calcified tissue, it may not be possiblefor the operator to generate enough force to properly deploy the RFelectrodes.

There is a need, therefore, for an RF tissue ablation device thatinduces minimal tissue trauma, and for which correct placement of thedevice can be readily ascertained. There is a need for an RF tissueablation device that is easily operated using only one hand, therebyleaving the operator's other hand free for other uses such as operatinga medical imaging device or managing the delivery of radiofrequencyenergy. There is also need for methods of RF electrode deployment otherthan manual deployment, so that the RF electrodes may be fully deployedin dense or calcified tissue.

An RF tissue ablation device has been developed to address one or moreof these needs. The device has an introducer having a proximal portionand a distal portion, and a plurality of RF electrodes that arepositionable in a nondeployed state within the introducer. The RFelectrodes are also positionable in the deployed state. The deployedstate occurs when an electrode advancement element, operably connectedto the RF electrodes, advances the RF electrodes from the introducerinto the subject's tissue. In some embodiments, the electrodeadvancement element includes a spring-loaded element to advance the RFelectrodes into the deployed state. The electrode advancement elementmay be actuated by a triggering device.

In some embodiments, the device has an occluder that substantiallyoccludes the introducer, thereby reducing tissue injury as the device isinserted into a subject. In some embodiments, the occluder is a plug,which may be comprised of a biocompatible material or materials, such ascollagen, gelatin, pectin, agar, arabic gum, xanthum gum, tragacanthgum, karaya alginic acid, karaya alginate salts, carrageenan, dextrin,starches, celluloses, polyvinyl alcohol, polyvinylpyrrolidone,polyethylene glycol, and mannans. The occluder may be displaced from thedistal end of the introducer as the device transitions from thenondeployed state to the deployed state.

In some embodiments, the device includes surface irregularities whichmay enhance the device's visibility by medical imaging techniques suchas ultrasound. The RF electrodes, the introducer, or both may havesurface irregularities.

Also disclosed is a method of ablating tissue in a subject, by insertingan introducer into the subject, deploying a plurality of RF electrodesfrom the introducer into the subject's tissue, and applying RF energy tothe RF electrodes. In certain embodiments of the method, the introduceris substantially occluded by an occluder such as a plug prior to RFelectrode deployment. In some embodiments, the plug is a biocompatiblematerial, such as collagen, gelatin, pectin, agar, arabic gum, xanthumgum, tragacanth gum, karaya alginic acid, karaya alginate salts,carrageenan, dextrin, starches, celluloses, polyvinyl alcohol,polyvinylpyrrolidone, polyethylene glycol, and mannans.

In some embodiments of the method, the RF electrodes are deployed by aspring-loaded element, which may be actuated by a triggering device onthe introducer. In other embodiments, either the introducer, the RFelectrodes, or both may be scored, and their positions may be confirmedby one or more medical imaging methods. The medical imaging methods usedto confirm the position of the introducer and/or RF electrodes may beultrasound, fluorscopy, computerized tomography, magnetic resonanceimaging, or any other suitable medical imaging technique.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view which illustrates one embodiment of the RFtissue ablation device, showing the device's nondeployed state.

FIG. 2 is a cross-sectional view of the RF tissue ablation device in itsnondeployed state, taken along line 2—2 of FIG. 1.

FIG. 3 shows the distal portion of the RF tissue ablation device, in thedevice's deployed state.

FIG. 4 illustrates a single RF electrode.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

As used herein, proximal refers to a portion of an instrument close toan operator, while distal refers to a portion of the instrument fartheraway from the operator. As used herein and in the claims, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

Referring now to the drawings, FIG. 1 illustrates one embodiment of theRF tissue ablation device of the present invention, in the device'snondeployed state. The embodiment consists of a housing 10 and anintroducer 12 which protrudes from the distal end of the housing.Introducer 12 is substantially hollow and has a proximal end and adistal end 14. Distal end 14 may be tapered or beveled to a point toenable percutaneous entry of the introducer into the target tissue.Adjacent to distal end 14, and substantially occluding distal end 14, isan occluder 16. The occluder may be a plug, which may be made of anymaterial, especially biocompatible material such as pectin, agar, arabicgum, xanthum gum, tragacanth gum, karaya alginic acid or its salt (e.g.,sodium alginate), carrageenan, dextrin, starches (corn starch, ricestarch, wheat starch, potato starch, pueraria starch, tapioca starch,carboxymethyl starch, hydroxypropyl starch, hydroxyethyl starch,chemically cross-linked starch, α-starch, and so on), celluloses(hydroxypropylmethyl cellulose, carboxymethyl cellulose, methylcellulose, methylethyl cellulose, hydroxypropyl cellulose, crystallinecellulose and so on), polyvinyl alcohol, polyvinylpyrrolidone,polyethylene glycol (macrogol), or mannans. A plurality of RF electrodes18 are contained within the introducer. Slide switch 20 protrudes fromthe housing and is constrained to move within slot 22. A firing button24 also protrudes from the housing for deployment of RF electrodes.

FIG. 2 illustrates a cross-section of the embodiment of FIG. 1, throughline 2—2. As in FIG. 1, the device's nondeployed state is illustrated.Housing 10 contains proximal end of introducer 12, which protrudes fromhousing distal end. Introducer's tapered distal end 14 tapers to a pointfor ease of insertion, and in the illustrated embodiment may besubstantially occluded by an occluder 16 such as a plug. A plurality ofRF electrodes 18 are contained within introducer 10. The proximal endsof RF electrodes 18 are attached to electrode advancement element 26,which consists of electrode driver 28 attached to proximal ends of RFelectrodes 18, spring 30 attached to electrode driver 28, and firingbutton 24 attached to proximal end of spring 30 and electrode driver 28,in a manner that maintains spring 30 in compressed position. Slideswitch 20 (shown in FIG. 1) is operably connected to electrode driver28. RF power wires 32 connect to proximal end of RF electrodes 18, passthrough center of spring 30, exit housing 10, and connect to RE powersupply 34.

In operation, introducer 12 is placed into the subject's tissue. Forexample, an area of skin overlying the subject's liver or other internalorgan may be cleansed with a povidone-iodine solution or otherappropriate antiseptic, and anesthetized with a local anesthetic such as1% lidocaine. The introducer's distal end 14 is inserted through theanesthetized skin to an appropriate depth and location, for example tothe approximate site of a primary or metastatic cancer lesion.Typically, the introducer's depth and location is determined with amedical imaging technique, such as ultrasound, magnetic resonanceimaging, computerized tomography, fluoroscopy, endoscopy and the like.Once the proper and/or desired introducer position is obtained, RFelectrode deployment is then triggered by actuating firing button 24.This releases spring 30 from its compressed position and driveselectrode driver 28 forward. RF electrodes 18 are pushed forward byelectrode driver 28, thus displacing plug 16 and forcing RF electrodesout distal end 14 of introducer 12. In an alternative embodiment, astylet may be attached at its proximal end to the electrode driver, andserve the function of driving the occluder out of the introducer. Thiswould relieve mechanical strain on the RF electrode tips that mightotherwise occur on impact with the occluder.

Once ejected from introducer 10 by electrode driver 28, RF electrodetips 18 array themselves in the target tissue, and their appropriateposition may be confirmed by a medical imaging technique such asultrasound, magnetic resonance imaging, computerized tomography,fluoroscopy, endoscopy and the like.

RF electrodes may be constructed from a variety of materials includingmemory metal alloys, as described in U.S. Pat. Nos. 5,935,123 and6,071,280, which are herein incorporated by reference in their entirety.For some applications, it may be advantageous for the RF electrodes tocurve outwards or inwards (evert or invert) as they are deployed, foroptimal array formation around the tissue to be ablated or reduced. Forsuch applications, preformed RF electrodes may be used as described inU.S. Pat. Nos. 5,827,276 and 5,855,576, which are herein incorporated byreference in their entirety.

FIG. 3 illustrates the device's deployed state. As in the nondeployedstate, introducer 12 contains RF electrodes 18 and electrode driver 28.FIG. 3 illustrates that after deployment, forward displacement ofelectrode driver 28 ejects plug 16 from distal end 14 of introducer 12,and arrays RF electrodes 18 within the target tissue.

Once the RE tissue ablation device assumes its deployed state, it isusually desirable for the operator or other individual to confirm thatthe RF electrodes are appropriately situated to accomplish their desiredfunction. This may be accomplished using any appropriate medical imagingtechnique, such as ultrasound. Occasionally, the operator may desire toredeploy the RF electrodes for better positioning or additionaltreatment. This may be accomplished by pulling back slide switch 20, forexample using the operator's thumb. This compresses spring 30 and causesfiring button 24 to catch and lock electrode driver 28, therebyre-establishing the device's nondeployed state as illustrated in FIGS. 1and 2. The operator may then redeploy the RF electrodes by actuatingfiring button 24. Those skilled in the art will observe that it is notessential that the RF electrodes be deployed by a spring-loadedmechanism. The RF electrodes may be advantageously deployed manually,for example by positioning the probes using slide switch 20. In general,for such manual positioning, spring 30 would be omitted from the device.Alternatively, the device could include a spring bypass switch thatwould enable either manual or spring-loaded deployment. In addition,those skilled in the art would recognize that the amount of force andextent of deployment could be readily varied by altering springcharacteristics.

For most applications, plug 16 is constructed from biocompatiblematerial such as collagen, gelatin, pectin, agar, arabic gum, xanthumgum, tragacanth gum, karaya alginic acid or its salt (e.g., sodiumalginate), carrageenan, dextrin, starches (corn starch, rice starch,wheat starch, potato starch, pueraria starch, tapioca starch,carboxymethyl starch, hydroxypropyl starch, hydroxyethyl starch,chemically cross-linked starch, α-starch, and so on), celluloses(hydroxypropylmethyl cellulose, carboxymethyl cellulose, methylcellulose, methylethyl cellulose, hydroxypropyl cellulose, crystallinecellulose and so on), polyvinyl alcohol, polyvinylpyrrolidone,polyethylene glycol (macrogol), or mannans. The materials can be usedsingly or in an appropriate combination. In some applications, it isadvantageous for the melting point of the plug material to besufficiently low such that during device operation, the heat generatedby the device melts the plug. Alternatively, the plug may melt, dissolveor otherwise degrade without the need for heat application.

To enhance ultrasonic visibility of RF electrodes, an introducer and/orRF electrodes may be provided with surface irregularities. Such surfaceirregularities enhance the return of sound waves to an ultrasoundtransducer, by increasing the amount of surface area appropriatelyoriented to receive sound waves and reflect them. The surfaceirregularities may be in virtually any regular or irregular arrangement,may be elevations or depressions in the surface, and may becircumferential or partial. FIG. 4 illustrates one embodiment of an RFelectrode with echogenic surface irregularities, namely an indented RFelectrode. RF electrode 18 has a series of noncircumferential notches 36that indent the electrode. The indentations create additional surfacesthat increase the amount of ultrasonic reflection and aid inlocalization of the deployed RF electrodes. Although FIG. 4 illustratessubstantial notches, the electrode's surface irregularities may in factbe quite minimal. For example, just a few fine serrations on anelectrode will substantially enhance ultrasonic visibility.

In view of the many possible embodiments to which the principles of theinvention may be applied, it should be recognized that the illustratedembodiments are only particular examples of the invention and should notbe taken as a limitation on the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

1. A tissue ablation device, comprising: an introducer having a proximalportion and a distal portion; one or more RF electrodes movable betweena nondeployed state within the introducer, and a deployed state in whichthe electrodes extend from the distal portion of the introducer; anelectrode advancement element coupled to the RF electrodes and capableof moving the RF electrodes between the nondeployed state and thedeployed state; and an occluder that occludes the distal portion of theintroducer when the electrode device is in the nondeployed state,wherein the occluder comprises a plug of biocompatible material mountedfor ejection from the distal portion of the introducer when theelectrodes are moved to the deployed state.
 2. The tissue ablationdevice of claim 1, further comprising surface irregularities on theintroducer.
 3. The tissue ablation device of claim 1, further comprisingsurface irregularities on one or more RF electrodes.
 4. The tissueablation device of claim 1, wherein the electrode advancement elementcomprises a spring-loaded element that advances the electrode devicefrom the nondeployed state to the deployed state.
 5. The tissue ablationdevice of claim 4 wherein the spring-loaded element is capable of beingactuated by a triggering device on the introducer.
 6. The tissueablation device of claim 1, further comprising a housing configured toenclose a proximal end of the introducer and at least a portion of theelectrode advancement element.
 7. The tissue ablation device of claim 6,wherein the housing and the electrode advancement element are configuredto be operable using a single hand.
 8. The tissue ablation device ofclaim 6, wherein the electrode advancement element comprises aspring-loaded element configured to deploy the electrodes through adistal end of the introducer upon actuation of a firing button, thefiring button being positioned on an exterior of the housing.
 9. Thetissue ablation device of claim 8, further comprising a slide switchcoupled to the electrode advancement element and operable to move the RFelectrodes to a nondeployed state, thereby compressing the spring-loadedelement.
 10. The tissue ablation device of claim 1, wherein the occluderis positioned at a distal end of the introducer.
 11. The tissue ablationdevice of claim 10, wherein the occluder and the distal end of theintroducer are beveled.
 12. The tissue ablation device of claim 1,wherein the occluder comprises a material that melts from heat generatedduring operation of the tissue ablation device.
 13. A tissue ablationdevice, comprising: an introducer having a proximal portion and a distalportion; one or more RF electrodes movable between a nondeployed statewithin the introducer, and a deployed state in which the electrodesextend from the distal portion of the introducer; an electrodeadvancement element coupled to the RF electrodes and capable of movingthe RF electrodes between the nondeployed state and the deployed state;and an occluder that occludes the distal portion of the introducer whenthe electrode device is in the nondeployed state, the occludercomprising a plug of biocompatible material, wherein the biocompatiblematerial is selected from the group consisting of: collagen, gelatin,pectin, agar, arabic gum, xanthum gum, tragacanth gum, karaya alginicacid, karaya alginate salts, carrageenan, dextrin, starches, celluloses,polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, andmannans.
 14. A method of ablating tissue in a subject, comprising:inserting an introducer into the subject; deploying a plurality of RFelectrodes from the introducer into the subject's tissue; and applyingRF energy to the RF electrodes; wherein prior to deployment of the RFelectrodes, the introducer's distal end is occluded by an occluder, andthe occluder comprises a plug of biocompatible material mounted forejection from the distal end of the introducer when the electrodes aredeployed.
 15. The method of claim 14, wherein the introducer has surfaceirregularities.
 16. The method of claim 14, wherein one or more of theRF electrodes has surface irregularities.
 17. The method of claim 14,wherein the RF electrodes are deployed by a spring-loaded element. 18.The method of claim 17, wherein the spring-loaded element is capable ofbeing actuated by a triggering device.
 19. The method of claim 14,wherein the position of the introducer is confirmed by one or moremedical imaging methods.
 20. The method of claim 14, wherein theposition of one or more RF electrodes is confirmed by one or moremedical imaging methods.
 21. The method of claim 19 or claim 20, whereinthe medical imaging method is selected from the group consisting ofultrasound, fluoroscopy, computerized tomography, endoscopy and magneticresonance imaging.
 22. The method of claim 14, wherein deploying theplurality of RF electrodes ejects the occluder from the distal end ofthe introducer and into the subject.
 23. The method of claim 22, furthercomprising melting the occluder ejected from the distal end of theintroducer with heat generated from the RF energy applied to the RFelectrodes.
 24. The method of claim 22, wherein inserting the introducerinto the subject and deploying the plurality of RF electrodes isperformed using a single hand of an operator.
 25. The method of claim14, further comprising: moving the plurality of RF electrodes back to anondeployed state; and repositioning the introducer in the subject. 26.The method of claim 25, wherein the moving and repositioning areperformed using a single hand of an operator.
 27. A method of ablatingtissue in a subject, comprising: inserting an introducer into thesubject; deploying a plurality of RF electrodes from the introducer intothe subject's tissue; and applying RF energy to the RF electrodes;wherein prior to deployment of the RF electrodes, the introducer'sdistal end is occluded by an occluder, the occluder comprising a plug ofbiocompatible material, wherein the biocompatible material is selectedfrom the group consisting of: collagen, gelatin, pectin, agar, arabicgum, xanthum gum, tragacanth gum, karaya alginic acid, karaya alginatesalts, carrageenan, dextrin, starches, celluloses, polyvinyl alcohol,polyvinylpyrrolidone, polyethylene glycol, and mannans.
 28. The methodof claim 27, wherein the position of the introducer, one or more of theRF electrodes, or both the introducer and the one or more of the RFelectrodes is confirmed by one or more medical imaging methods.
 29. Themethod of claim 27, wherein deploying the plurality of RF electrodesejects the occluder from the distal end of the introducer and into thesubject.
 30. The method of claim 29, further comprising melting theoccluder ejected from the distal end of the introducer with heatgenerated from the RF energy applied to the RF electrodes.
 31. Themethod of claim 27, wherein inserting the introducer into the subjectand deploying the plurality of RF electrodes is performed using a singlehand of an operator.